Removal of condensate from dryer rolls



R. CLEMENTS REMOVAL OF' CONDENSATE FROM DRYER ROLLS Nov. 5, 195.7

Filed Jan. e, 1955 2 Sheets-Sheet 1 Nov. 5, 1957 R. CLI-:MENTS REMOVALOF CONDENSATE FROM DRYER ROLLS 2 Sheets-Sheet 2 Filed Jan. 6, 1955INVENTOR.

/PA 1ro/eo CLEMENTS.

United States Patent() REMOVAL OF CONDENSATE FROM DRYER ROLLS RaifordClements, Jacksonville, Fla., assignor to St. Regis Paper Company, NewYork, N. Y., a corporation of New York Application January 6, 1955,Serial No. 480,205

9 Claims. (Cl. 34-41) This invention relates to methods and equipmentfor removing condensate from dryer rolls, which are internally steamheated, the invention among other possibilities being particularlyadapted for use in connection with the dryer rolls of high speed papermaking machines.

In paper making machines, the paper after being formed is customarilyconducted over a series of dryer rolls, each of which is generallyheated by circulating steam through the interiors thereof, with theresult that considerable proportions of the steam become condensedWithin the rolls. If the machine is one which operates at a relativelylow or modera-te speed, such condensate will remain as a socalled puddleat the bottom of the roll cavity and in that position a constantpressure differential between the steam inlet and outlet connections tothe roll will serve efficiently to remove such condensate withoutsubstantial difficulties and according to well-known methods. However,if the machine speed is increased, as is the case with many modern papermachines, to an extent such that centrifugal force will cause thecondensate to rim or to be distributed around on the interior surface ofthe roll, then serious diculties tend to occur with known equipment forcontrolling condensate conditions in such rolls. These difficulties willbe even greater if the paper machine is one which has from time to timeto be operated at different speeds for forming different kinds of paperrequiring more or less drying heat and at different rates of drying. Asa consequence, in the usual present-day high speed paper making machine,accumulations 'of condensate in the rolls become so great that from timeto time it is necessary to stop the machine and to blow out thecondensate. Otherwise as the rim of water in the roll increases inthickness, the efficiency of the roll as a drying unit will rapidlydecrease. Furthermore, as the mass -of water in each roll increases, thepower necessary to drive the machine is greatly increased due toincreased friction at the roll bearings. Also, as the masses of water inthe rolls increase, turbulent conditions may arise whereby the inertiaof the roll plus its content of water will not be symmetricallydistributed around the axis of the roll, thereby causing variations orsurges in the driving power required and consequent roll speedvariations, to the point where the paper web may be broken. The loss ofmachine time and the paper losses resulting from paper breakage on apaper machine, are of course very expensive, as is also the shuttingdown of such machines in order to remove the condensate.

In order that the steam in such dryer rolls may be efficiently used, itis preferable to introduce same at a temperature and pressure such thatthe greater portion thereof will become condensed in the rolls and thusgive 'up its latent heat. To achieve this condition, it becomesimportant to control as closely as possible the pressure differentialbetween the inlet and outlet connections for the rolls, and so that suchdifferential will effectively control the rate of flow through the rollsfor a given set of conditions without waste of steam and while avoidingexcessive accumulations of condensate. Heretofore i-t has ice also beenwell-known practice for eicient utilization of the dryer roll steam todivide the large number of rolls into groups with provision for adifferent steam pressure for each group and with facilities forwithdrawing condensate separately from each group. But any attemptproperly to control such an extensive system manually involvesinaccuracies and uncertainties, particularly if the paper machine speedis changed from time to time. This has tended to result in the practiceof making the pressure differential high enough to insure propercondensate removal under all of the varying conditions under which themachine is operated, but with the consequence of. quite inefficient useof the steam.

With the present invention, the above-explained difficulties have beeneliminated by providing a method and equipment which will preferablyautomatically control the pressure differential at varying machinespeeds and at all of the dryer rolls, and if desired with a differentpressure level for succeeding groups of rolls as is required for mostefficient use of the steam. If the machine is running fast enough ysothat the condensate in the rolls will rim, I have found that the mostimportant factor in determining the most efficient pressure differentialto be used is the peripheral velocity of the roll and the consequenteffect of centrifugal force tending to hold the condensate against theinterior surface of the roll and preventing its easy removal. Suchcentrifugal force will vary according to the well-known formula where Fis the centrifugal force upon a mass of the Water; M is the mass ofwater; V is a velocity equivalent to the effective linear velocity ofthe mass of water; and R is the effective radius of the mass of thewater. Thus assuming that M and R are maintained substantially constant,the force effective in preventing withdrawal of the condensate Varies asthe square of the velocity of `the water and hence it will be apparentthat at increased machine speeds, the pressure differential necessary toforce out the condensate must also increase in accordance with thesquare of the velocity, -that is to say, substantially in accordancewith the square of the velocity of the paper running through the machineover the exterior surfaces of the rolls. Tests of the present inventionhave proven that such other factors as might be expected to effect theideal pressure differential, are substantially insignificant as comparedwith .the machine speed, when the machine speed is high or relativelyhigh. Hence in accordance with the present invention, provision is madefor varying the pressure differential at the dryer rolls, preferablyautomatically, in accordance with the square of the linear velocity ofthe paper. This may be accomplished by a variety of different types ofknown valve controlling devices, that is, devices which, in response tochanges of the machine speed, will adjust the pressure differentialcontrol valves in accordance with a square law, for example well-knownforms of tachometer-generators may be used with electro-pneu.- maticconverters or with proper amplification to actuate electrically drivenvalves according to the square law. However, I have found that a veryconvenient way 0facccmplishing this result, with inexpensive apparatus,is by adjusting the differential pressure control valves responsive ltoVariations in the liquid head in the headbox of a Fourdrinier type ofpaper making machine. According to the formula VZ H --25 l the pressurehead H of the liquid in the headbox is equal to the square of thespouting velocity at the slice of the headbox, divided by 2g. In theusual paper making ma? chille,v such spouting velocity is substantiallyequal to the speed of -the paper through the machine, and since thefactor 2g is a constant, the pressure head in the headbox gives* aAmeasure which varies proportionately with the Square of the velocityofthe paper through the machine. Hence, such measure may be used tocontrol the desired dryer roll pressure differential so as also to varysuch differential according to thesquare of the dryer roll surfacespeed;

Various further and more specific objects, features and advantages ofthe invention will appear from the description given below, taken inconnection with the accompanying drawings illustrating by way of examplecertain preferred'forms of the invention.

Inthe drawings:

lFigure l is a schematic diagram of a Fourdrinier type of paper makingmachine and showing the position of a master differential pressurecontroller at the headbox, in accordance with the presently preferredform of the invention, such controller being used to control the dryerroll pressure differentials; .lFigure 2 is a schematic diagram showingthe various groups of dryer rolls of a typical high speed large papermaking machine and with thc various connections, valves and controllingdevices schematically shown in accordance with a preferred example ofthe invention;

Figure 3 is a schematic diagram of certain of the differential pressurecontrolling equipment used for the system of Figure 2;

Figure 3a shows a valve like one of the valves in Figure 3 but modifiedas required when the control equipment of Figure 3 is used in certainparts of the system;

Figure 4 is a vertical sectional view through a typical one of the dryerrolls showing the steam inlet and condensate withdrawal connections; and

Figure -5 is a schematic diagram of an alternative arrangement forcontrolling the pressure differential valves.

Referring now to Fig. 1 in further detail, there is here shownschematically a typical paper making machine havinga headbox asindicated, from which the pulp stock flows through a slice onto theFourdrinier wire, the paper as formed then passing through any knownform of press section and thence through a dryer section comprising anextensive series of dryer rolls such as schematically indicated in Fig.2. At the headbox a master differential pressure controller (one form ofwhich will be hereinafter described in further detail) is indicated ashaving a pressure connection 11 to the liquid at the bottom of theheadbox. This controller, which in one well-known commercially availableform, for example, may comprise a Foxboro differential pressure cell, isso constructed and arranged that responsive to any variations in thepressure head of the liquid in the headbox, it will transmitcorresponding variations as through a pressure connection 12 todifferential pressure control apparatus hereinafter explained inconnection with Fig. 2. That is, the pressure transmitted through theconnection 12 will vary in accordance with the square of the velocity ofthe stock emanating from the slice. Thus the pressure transmitted variessubstantially in accordance with the square of the velocity of the paperbeing made on the machine and in accordance with the square of thevelocity circumferenttiallry of the surfaces of the dryer rolls overwhich the paper passes. Accordingly, if the pressure variations in theconnection 12 are now used to vary directly in accordance therewith thepressure differentials of the steam enter-ing and leaving the dryerrolls, then such differentials will consequently be varied according toV2 as above explained.

Referring now to Fig. 2, there is here shown schematically the dryersection of a typical large high speed paper machine equipped inaccordance with the invention and in whichthe dryer rolls are dividedinto groups-13, 14, 15, 1,6, 1'7 and 18. Live steam for these rolls isadmitted through a steam main 19 connected to abranch lineas at 20 forroll group 14, branch line 21 for roll group 16 and branch line 22 forroll group 17. The other roll groups 13, 15 and 18, as hereinafterexplained, receive steam indirectly respectively from groups 14, 16 and17 The control connections for roll groups 13 and 14 will now bedescribed and it will be apparent that like control connections areprovided for roll groups 15 and 16 as well as for groups 17 and 18.

From branch line 20, connections 24 conduct the live steam in through asuitable axial conduit of well-known form, as indicated in the sectionalview of Fig. 4, and concentrically with the steam inlet connection ofthe roll, there is a conduit outlet connection 25. The inlet openingslto such condensate connections are located as at 25' (Fig. 4) close tothe inner wall of the dryer roll, for example about one-half inch fromthe wall surface, theA apparatus preferably being so constructed andarranged that the condensate will be kept down to a layer, as at 26,which will be only a fraction of an inch in thickness.

From the outlet connections 25, the condensate is collected in a ashtank or receiver as at 27, where its temperature is lowered so thatsteam is flashed off at the lower pressure leaving a body of condensate28. The steam is conducted through a connection 29 to a header 30connected to the steam inlets 32 for roll group 13. The header 30 isalso connected through a pressure-operated differential control valve 31to the branch main 20. The condensate is withdrawn from roll group 13through connections 33 and thence to another receiver 34, the lower partof which will contain a body of condensate, whereas noncondensable gasesand some flashed steam will be drawn through connection 35 from theupper part of this receiver. Between the flash tank 27 and the receiver34 a connection with a control valve 36 is provided. This valve may, asschematically indicated, be controlled by a float in flash tank 28 so asnot to allow the condensate level in such tank to fall low enough topermit steam to pass directly into receiver 34.

Condensate is pumped from receiver 34 as by a pump 37 through a controlvalve 38 and thence through a line 39 back to the powerhouse or acentral condensate collecting point. Valve 38 is also float-controlled,as schematically indicated by the height of the liquid in receiver 34and whereby the liquid will never be wholly withdrawn, which wouldpermit steam to pass outthrough the pump to the condensate line 39.

The steam from receiver 34, which passes out through connection 35, thenpasses through a differential pressure control valve 40 to a dischargeline 41 which in the particular example here being described, issubjected to vacuum. The connection 41 may pass into a heat exchanger orcondenser 42 which cools the remaining steam below the flashingtemperature before it goes'into another receiver 43. Condensate isremoved from receiver 43 as by a pump 44 which discharges through a controll valve 45 to a condensate discharge line which may be connectedto the discharge line 39 above referred to. The valve 45 is, asschematically shown, controlled by a oat in receiver 43 so that a bodyof liquid will be maintained in this tank as a seal. The upper part oftank 43 has a connection 47 running to a vacuum pump 48. The purpose ofthis vacuum pump is to maintain a sulciently low pressure on thecondensate side of the system, as compared with the live steam inlet,.so that an adequate pressure differential may be obtained across thedryer rolls without an excessively high live steam inlet pressure. Also,non-condensable gases pass out through the vacuum pump 48.

In Fig. 2, the master differential pressure controller, as indicated at10, is connected by pneumatic tubing (indicated by dashA lines) topneumatic receiver controllers for each group. of the dryer rolls. Thatis, for dryer roll group 14, the receiver controller is indicated at'50and for the roller group 13, the controller is indicated at 51. Themaster controller 10 in conjunction with the controller 50, for example,will now be described in connection with Fig. 3, which schematicallyillustrates the esential parts of this equipment. The pressure at thebottom of the headbox is brought through pipe 11 to a chamber 52 havinga diaphragm 53 to which is pivotally connected a lever 54 having a vane55 located in the path of an air jet from an orifice 56. The orifice 56is arranged to release variable amounts of air from pipe 12 which isconnected to a suitable source of air at constant pressure, the amountof air released depending upon the proximity of the vane S to theorifice. Thus the lever 54 which may be fulcrumed as at 57 is normallyheld by a spring 53 in a position spaced close to the orifice but whenthe headbox pressure against the diaphragm 53 is increased, the vane 55will move closer to the orifice, thereby checking the escape of airtherethrough and conversely when the headbox pressure is reduced, thevane 55 will move to a position more remote from the orifice, allowingmore air to escape. Thus the air as supplied through pipe 12 Will varyin pressure in accordance with the variations in pressure at theheadbox. The device 50 above referred to may be comprised of theapparatus shown in the upper part of Fig. 3. That is, a pipe 6i) isarranged to bring the steam branch line 20 into communication with adiaphragm chamber 61. A pipe 62 is arranged to bring the steam pipe 30(Fig. 2) into communication with a diaphragm chamber 63. That is,diaphragm chambers 61 and 63, respectively, are connected to the highand the lower pressure sides of control valve 31. A pivotally mountedlever 64 is arranged to be tilted in either direction by the diaphragms61, 63 and to an extent depending on the relative pressures in `thesteam pipes 20 and 30. The lever 64 has a vane 65 opposed to an air jetfrom an orifice 66, this orifice being arranged to discharge variableamounts of air from an air line 67, which extends from a suitable sourceof constant air pressure to a Bourdon tube or the like 68. Thusdepending upon the relative pressures at opposite sides of the controlvalve 31, this Bourdon tube will be expanded or contracted. The movableend of the Bourdon tube may be connected as by link means 69 to a lever70. One end of this lever is arranged to be movable by a bellows 71which communicates with the above-mentioned pipe 12. The other end oflever 70 carries a vane 72 arranged in opposed relation to an orifice 73which discharges air from a pipe 74, which pipe runs from a source ofconstant air pressure to the pressure diaphagm-operated valve 31. Itwill be noted that the pressure-operated valve 31 is arranged to bemoved toward closed position whenever the pressure in pipe 74 increases,as when orifice 73 becomes blocked.

The operation of the arrangement of Fig. 3 is as follows. When themaster controller 10, for example `due to increased headbox pressure,causes the pressure in pipe 12 to increase, then the bellows 71 willexpand, thereby moving the vane 72 closer to orifice 73 with the resultthat the pressure in pipe 74 increases and the valve 31 is moved towardclosed position. This, of course, occurs when the paper machine speedincreases, at which time the pressure drop between the steam inlet andoutlet connections for the group of rolls 14 should be increased inproportion to the square of the machine speed. Thus when valve 31 tendsto close, less steam will flow from branch line 20 into steam pipe 30and consequently the pressure in the latter pipe will decrease. Sincepipe 30 communicates with the condensate outlets of rolls 1,4, therewill result a greater pressure drop between the inlets and outlets ofrolls 14, the increase in pressure drop being to the degree required byreason of the increased centrifugal force on the condensate which has tobe overcome to withdraw such condensate. It should be mentioned that thepressure in branch line 20 may be regulated at a constant value as by apressure-regulating valve 80, or such valve may be controlled by any ofthe various well-known mechanisms for varying dryer steam pressure inaccordance with the desired degree of dryness of the paper. Similarly,valves and 80" for the branch lines 21 and 22 may comprise eitherconstant pressure-regulated valves or valves connected to such apparatusto vary the steam pressure according to the desired dryness ofthe paper.

Referring further now to the upper portion of Fig. 3, let us assume thatthe pressure in line 60 (as controlled by valve 80) should rise. Thenthe vane 65 would move to release more air from orifice 66 in line 67thereby lowering the pressure in the Bourdon tube 68 and acting to movevane 72 so as to release more air through orifice 73 from line 74 andthus tending to open the valve 31 further. This in turn will tend toincrease the pressure in line 30 and thus react in diaphragm chamber 63to bring vane 65 back to normal position with respect to orifice 66.Thus the equipment at the upper part of Fig. 3 permits the maintainingof the desired pressure differential as determined by controller 10regardless of the temperature level at which the live steam is admittedthrough valve 80 to the branch line 20.

The construction and operation of the receiver controller meansindicated at 51 (Fig. 2) may be the same as above described inconnection with Fig. 3 with one exception. That is, the pressurediaphragm-operated valve 40 to which this controller is connected(instead of a valve like that at 31) is, as shown in Fig. 3a, arrangedto be opened more widely when the pressure applied thereto is increasedand conversely to move toward closed position when the pressure appliedthereto is decreased. This difference arises from the fact that whilethe valve 31 is at the inlet steam connection to rolls 14, the valve 40is in the condensate outlet side of the roll group 13 in which thepressure differential is to be controlled by the latter valve. In otherwords, valve 31 is arranged to bleed off steam into the outlet side ofrolls 14, whereas valve 40 is arranged to tend to shut off steam passingfrom the outlet side of rolls 13.

As will be apparent from Fig. 2, all of the control connections for rollgroups 15 and 16 respectively may be in substance duplicates of thosefor roll groups 13 and 14 and .same are identified by the same referencecharacters but accompanied by prime marks. Similarly, the controlconnections for roll groups 18 and 17 respectively are like those forgroups 13 and 14 and are identified by the same reference charactersaccompanied by double prime marks.

In a typical case, the live steam pressure as controlled by valve 80 maybe 20 pounds and the pressure differential across roll group 14 mayamount to 5 pounds, with a consequence that the pressure on the inletside of roll group 13 will be l5 pounds; and if the pressuredifferential across roll group 13 is also to be 5 pounds, then thepressure in the outlet pipes 33 in advance of the control valve 40 willbe l0 pounds, whereas following the valve 40 there may, for example, bel0 inches of vacuum. If for example, properly to dry a given web ofpaper, the live steam pressure in branch line 20 has to be raised tosay30 pounds then the steam pressure differentials across the rollgroups may still be maintained at 5 pounds, although the inlet andoutlet pressures for roll group 13 would then be 25 pounds and 20 poundsrespectively.

Similar pressures and pressure differentials may be used for roll groups15 to 18, inclusive, although in some cases it will be desirable tointroduce the live steam at a higher temperature level in the rollgroups 15 and 16 and at a still higher temperature level in the finalgroups 17 and 18, under the control of valves 80 and 30, but in eachcase with the same preferred differential.

It will be understood that with paper machines having different numbersof dryer rolls, same may be grouped in various ways as may be preferredand with a greater or lesser number of groups than shown in Fig. 2.

As above mentioned, the pressure differentials may be varied accordingto the square of the velocity of the paper in ways other than by amaster controller locatedl at-the headbox as above described. Forexample, with cylinder type machines which have no headbox with which acontroller such as at could be used, then the arrangement, such asschematically shown in Fig. 5, might be adopted. Here, as indicated, agenerator such as a small D. C. generator is driven by one of the driveshafts of the paper machine so as to produce a voltage varying accordingto the machine speed, which voltage is sensed by a voltmeter type ofinstrument as schematically shown. This instrument may be arranged torotate a so-called square-to-linear conversion cam. A pivotally mountedcam follower, as shown at 90, is normally held by a spring against thiscam and the cam follower provides a vane opposed to an orifice 91 forbleeding air from an air line 92. The air line 92 comprises analternative for the above-described air line 12 in Fig. 3 and serves toconduct pressure variations into bellows as at 71 of Fig. 3.

While the invention has been described as applied to the dryer rolls ofa paper machine, it will be understood that similar equipment may beused for controlling the removal of condensate in various other forms ofrolls which are heated by a condensable fluid such for example as therolls of paper coating machines, and textile and printing machinery.

While the method of the invention is described above in connection withequipment which functions automatically to carry out the method afterthe making of predetermined adjustments, it will be understood that inits broader aspects the method might also be carried out by manuallyadjusting the pressure differential control valves so as to vary thepressure differential in proportion to-the square of the velocity of theroll surface. However, in the usual large paper machine in which it isadvisable to divide the rolls into groups as above explained, there willbe so many control valves that accurate manual adjustment would bedifficult, particularly in case of high speed paper machines in whichfor one reason or another the speed may vary from time to time withconsequent great changes in the centrifugal force effects requiringreadjustment of the valves.

Although certain particular embodiments of the invention are hereindisclosed for purposes of explanation, various further modificationsthereof, after study of this specification, will be apparent to thoseskilled in the art to which the invention pertains. Reference shouldaccordingly be had to the appended claims in determining the scope ofthe invention. What is claimed and desired to be secured by LettersPatent is:

l. A method for controlling the removal of condensate from afluid-heated rapidly-rotating roll to which a condensable heating fluidis admitted and allowed to condense, the condensate being distributed bycentrifugal force around on the interior surface of the roll and thenbeing withdrawn, which method comprises: establishing a predetermineddifferential as between the fluid inlet and outlet pressures and uponvarying the speed of rotation of the roll, varying such differentialapproximately in proportion to the square of the velocity of the surfaceof the roll.

2. A method for controlling the removal of condensate fromrapidly-rotating dryer rolls of a paper machine to which steam isadmitted and allowed to condense, the condensate being distributed bycentrifugal force around on the interior surface of the rolls and thenbeing withdrawn, which method comprises: establishing a predetermineddifferential as between the steam inlet and condensate outlet pressuresand upon varying the speed of the machine varying such differentialapproximately in proportion to the square of the velocity of the surfaceof the rolls.

3. A method for controlling the removal of condensate from 'steam heateddryer rolls of a Fourdrinier type of paper machine in which the stockunder the pressure head in the headbox is discharged from the slice atapproximately the speed of travel of the paper over the rolls throughthe machine, which method comprises: applying suction to withdraw suchcondensate from the dryer rolls, which suction is effectively variedsubstantially directly in proportion to variations in said pressure headwhen said pressure head is varied to vary the discharge velocity at theslice to correspond to varying machine speeds.

4. A method for controlling the heating of rapidly rotating rolls whichare heated by introducing a condensable fluid so that the condensate isdistributed by centrifugal force around on the interior of the rolls andthen withdrawn, which method comprises: introducing suchfluid into therolls under predetermined controlled but adjustable pressure,establishing a predetermined differential as between the inlet andcondensate outlet pressures and upon varying the speed of rotation ofthe rolls, varying such differential approximately in proportion to thesquare of the velocity of the surface of the rolls and upon adjustingthe inlet pressure, also adjusting the pressure at which the condensateis withdrawn to maintain said differential substantially constant.

5. A method for controlling the heating of, and removal of condensatefrom, rapidly rotating web dryer rolls which are heated by introducing acondensible fluid into a first group of the rolls from which thecondensate is withdrawn and allowed to vaporize at a lower pressure andthen is introduced into a second group of the rolls from which theresulting recondensed fluid is also withdrawn, which method comprises:establishing a predetermined pressure differential as between the fluidinlet and outlet pressures for said first group of rolls and also forsaid second group of rolls and upon varying the speed of rotation of therolls, varying such differential for the first group by by-passingsufiicient fluid from the inlets to the first group to the inletconnections for the second group whereby the differential for the firstgroup is varied approximately in proportion to the square of thevelocity of the surface speed of the rolls, and varying suchdifferential for the second group by varying the discharge of fluidtherefrom to an extent whereby such differential for the second group isalso varied approximately in proportion to the square of said velocity.

6. A method for controlling the heating of, and removal of condensatefrom, rapidly rotating web dryer rolls which are heated by introducing acondensable fluid into various groups of the rolls at differentcontrolled but adjustable pressures, from which webs the condensate iswithdrawn and allowed to vaporize at lower pressures and then isintroduced into various other groups of the rolls respectively fromwhich the resulting recondensed fluid is also withdrawn, which methodcomprises: establishing a predetermined pressure differential as betweenthe fluid inlet and outlet pressures for all of said first mentionedgroups of rolls and also for said other groups; and upon varying thespeed of rotation of the rolls, or upon adjusting said first mentionedpressures, varying such differential for the first mentioned groups bybypassing sufficient fluid from the inlets thereof to the inletconnections for said other groups respectively whereby the differentialfor the first mentioned groups is varied approximately in proportion tovthe square of the velocity of the surface speed of the rolls but ismaintained substantially constant if said velocity is unchanged; andvarying such differential for said other groups by varying the dischargeof fluid therefrom to an extent whereby such differential for such othergroups is also varied approximately in proportion to the square of saidvelocity but is lalso maintained substantially constant if said velocityis unchanged.

7. Apparatus for controlling the heating of and the removal ofcondensate from rapidly rotating web dryer rolls which are heated bycondensable fluid, which apparatus comprises: connections forintroducing the fluid .and withdrawing the condensate from the rolls;pressure regulating valve means for normally maintaining a predeterminedpressure differential as between the inlet and outlet connections; andmeans for establishing and maintaining a control medium which variessubstantially in proportion to the square of the velocity of the surfacespeed of the rolls, such valve means being constructed and arranged tobe responsive to vary said differential approximately directly inaccordance with the variations of said control medium whereby saiddifferential is varied approximately in accordance with the variationsof centrifugal force on the condensate in the rolls.

8. Apparatus for controlling the heating of and the removal ofcondensate from rapidly rotating steam heated dryer rolls of aFourdrinier type paper machine having a head box with slice for variablyfeeding stock onto the wire according to the machine speed, whichapparatus comprises: connections for introducing the steam andwithdrawing the condensate from the rolls; pressure regulating valvemeans for normally maintaining a predetermined pressure differential asbetween the inlet and outlet connections; and means for establishing andmaintaining a control medium which varies substantially according to thepressure head in the headbox and thus approximately in proportion .tothe square of the velocity of the surface speed of the rolls, such valvemeans being constructed and arranged to be responsive to vary saiddifferential directly in proportion to variations of said control mediumwhereby said differential is varied approximately in accordance with thevariations of centrifugal force on .the condensate in the rolls.

9. Apparatus for controlling the heating of and the removal ofcondensate from rapidly rotating web dryer rolls which are heated bycondensable fluid, which apparatus comprises: connections forintroducing the uid and withdrawing the condensate from the rolls;pressure regulating valve means for normally maintaining a predeterminedpressure differential as between the inlet and outlet connections, butat different pressure levels for different groups of said rolls; meansfor establishing and maintaining a control medium which variessubstantially in proportion to the square of the velocity of the surfacespeed of the rolls, such valve means being constructed and arranged tobe responsive to said control medium to vary said dierential for all theroll groups approximately in accordance with the variations ofcentrifugal force on the condensate in the rolls.

References Cited in the lile of this patent UNITED STATES PATENTS1,347,723 Wagner July 27, 1920 1,531,744 Farnsworth Mar. 31, 19251,674,845 Stickle June 26, 1928 1,695,972 Ohlin Dec. 18, 1928 2,150,132Sandwell Mar. 7, 1939

